Internal combustion engine

ABSTRACT

Disclosed herein is an internal combustion engine having a plurality of cylinders, a crankcase, a cylinder head and a cylinder-head cover, the cylinder head being formed from a cylinder-head lower part and a camshaft housing which is positioned between the cylinder-head cover and the cylinder-head lower part, and at least one camshaft and one sliding cam which can be displaced axially on the camshaft and has a slotted-guide section being provided for actuating gas exchange valves of the internal combustion engine, an actuator with an actuable pin being provided for bringing about an axial displacement of the sliding cam. The camshaft and the sliding cam are positioned in the camshaft housing. The camshaft, which is mounted rotatably for valve actuation, is arranged with the axially displaceable sliding cam in the camshaft housing in such a way that they can be attached to the cylinder-head lower part as one preassembled unit.

CROSS-REFERENCE TO RELATED APPLICATION

This U.S. patent application claims priority to German Patent Application DE102010036899.7, filed Aug. 6, 2010, which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to an internal combustion engine having a plurality of cylinders.

BACKGROUND OF THE INVENTION

In modern internal combustion engines, variable valve timing mechanisms are used to optimize the charge movement in the combustion chamber, by way of which variable valve timing mechanisms different valve strokes can be set for the gas exchange valves of the internal combustion engine. DE 196 11 641 C1, which is incorporated by reference herein, has disclosed a valve timing mechanism of an internal combustion engine, by way of which valve timing mechanism the actuation of a gas exchange valve with a plurality of different lifting cams is made possible. To this end, a sliding cam with a plurality of cam tracks is mounted fixedly on the camshaft so as to rotate with it but so as to be displaceable axially, which sliding cam has a lifting contour, into which an actuating element engages in the form of a pin for generating an axial displacement of the cam. As a result of the axial displacement of the cam, a different valve stroke is set for the respective gas exchange valve.

DE 10 2007 027 979 A1, which is incorporated by reference herein, has described a valve timing mechanism for gas exchange valves of an internal combustion engine with a camshaft tunnel bearing, which valve timing mechanism comprises cam pieces which can be displaced on a camshaft, a radial bearing of the camshaft being positioned between two sliding-cam pieces which are provided for the actuation of gas exchange valves of a cylinder. The previously known mountings of a valve timing mechanism with a sliding-cam assembly are complicated and afford restricted flexibility.

SUMMARY OF THE INVENTION

Disclosed herein is a simplified arrangement of a valve timing mechanism in a cylinder head of an internal combustion engine, in particular with regard to the positioning and the mounting of a sliding-cam system in the cylinder head.

According to one aspect of the invention, an internal combustion engine has a plurality of cylinders, a crankcase, a cylinder head and a cylinder-head cover, the cylinder head being formed from a cylinder-head lower part and a camshaft housing which is positioned between the cylinder-head cover and the cylinder-head lower part, and at least one camshaft and one sliding cam which can be displaced axially on the camshaft and has a slotted-guide section being provided for actuating gas exchange valves of the internal combustion engine, an actuator with an actuable pin being provided for bringing about an axial displacement of the sliding cam, characterized in that the camshaft and the sliding cam are positioned in the camshaft housing, it being possible for the camshaft which is mounted rotatably for valve actuation to be assembled with the axially displaceable sliding cam in the camshaft housing in such a way that the camshaft, the sliding cam and the camshaft housing form one preassembled unit which can be attached to the cylinder-head lower part.

The internal combustion engine is distinguished by the fact that the camshafts and the sliding cams are positioned in the camshaft housing, it being possible for the camshaft which is mounted rotatably for valve actuation to be assembled with the axially displaceable sliding cam in the camshaft housing in such a way that the camshaft, the sliding cam and the camshaft housing together form one preassembled unit which can be attached to the cylinder-head lower part. Advantageous accommodation of a valve timing mechanism therefore takes place with a compact sliding-cam device for the actuation of the gas exchange valves of a cylinder in a camshaft housing, which can be preassembled before the attachment of the camshaft housing to the cylinder-head lower part is carried out. This leads to simplified assembly of the internal combustion engine and therefore makes reliable, quality-assured and inexpensive production of the internal combustion engine possible on account of the simplified handling and the unit which is tested in advance and is preassembled.

As claimed in one refinement of the invention, the actuators which are provided for bringing about the axial displacement of the sliding cam are arranged in a lateral region of the camshaft housing. To this end, a lateral wall of the camshaft housing is expediently provided with a plurality of openings arranged in it for receiving the actuators. As a result of the lateral arrangement of the actuators, they can be introduced into the camshaft housing with less outlay than previously and the construction tolerances can be reduced, the said actuators then being accommodated in such a way that an overall height of a cylinder head is reduced to a minimum. This therefore brings about a particularly compact and simplified arrangement of the internal combustion engine, the connecting options of the actuators, for example to a control unit of the internal combustion engine, being simplified by the lateral openings which are provided to accommodate the actuators. Moreover, the design of the cylinder-head cover, in particular, can be of simplified configuration.

As claimed in one preferred refinement of the invention, each sliding cam is assigned an individual actuator per cylinder for the actuation of the inlet-side or outlet-side gas exchange valves. In particular, the sliding cam and the actuator are positioned in the camshaft housing spatially between two bearing points of the camshaft. At least two or three gas exchange valves can preferably be actuated by way of one sliding cam per cylinder, the slotted-guide section which is arranged on the sliding cam being positioned between two cam sections which in each case serve for the actuation of the gas exchange valves and in each case have a plurality of cam tracks. As a result, there is a compact sliding-cam form, by way of which the actuation of two gas exchange valves which are positioned close to one another can be brought about in a functionally reliable manner.

In a further refinement of the invention, the camshaft adjusting device and the drive wheel are connected to the camshaft, are arranged in the camshaft housing and advantageously form a part of the preassembled unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and combinations of features result from the description. Concrete exemplary embodiments of the invention are shown in simplified form in the drawing and are explained in greater detail in the following description. In the drawing:

FIG. 1 shows a diagrammatically illustrated internal combustion engine of the boxer type,

FIG. 2 shows a sectional view of the cylinder head of the internal combustion engine from FIG. 1,

FIG. 3 shows a further sectional view of the cylinder head of the internal combustion engine from FIG. 1,

FIG. 4 shows a perspective view of a camshaft housing of the internal combustion engine from FIG. 1 according to a first embodiment,

FIG. 5 shows a further perspective view of the internal combustion engine from FIG. 1 according to the first embodiment,

FIG. 6 shows a perspective view of a camshaft housing of the internal combustion engine as shown in FIG. 1, according to a second embodiment, and

FIG. 7 shows a perspective view of the camshaft housing of the internal combustion engine as shown in FIG. 1, with bearing devices which are configured integrally on the camshaft housing.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an internal combustion engine 1 of the boxer type which is formed from two cylinder rows 1 a and 1 b which are arranged horizontally. The internal combustion engine 1 comprises a crankcase 2 and in each case one cylinder head 3 per cylinder row 1 a and 1 b, which cylinder head 3 is delimited to the outside by a cylinder-head cover 4. The cylinder head 3 is assembled from a cylinder-head lower part 5 and a camshaft housing 6.

As shown in FIG. 2, an inlet camshaft 7 and an outlet camshaft 8 are mounted in the camshaft housing 6 for controlling gas exchange valves of the internal combustion engine 1. The camshaft housing 6 is attached as one preassembled unit to the cylinder-head lower part 5 and is screwed to the latter. After the mounting of the camshaft housing 6 on the cylinder-head lower part 5, the cylinder-head cover 4 is attached to the camshaft housing 6. A plurality of bolts 12 are provided for fastening the cylinder-head cover 4 to the camshaft housing 6.

Two inlet valves 9 and two outlet valves 10 are provided per cylinder, the inlet valves 9 being actuated in a controlled manner by the inlet camshaft 7 in a known way. The outlet valves 10 are actuated in a controlled manner by the outlet camshaft 8. To this end, the inlet camshaft 7 and the outlet camshaft 8 mounted in the camshaft housing 6 in each case have a plurality of sliding cams 13. FIG. 3 shows a sectional view through the inlet camshaft 7 which actuates the two inlet valves 9 with the aid of roller drag levers 21. As shown in FIG. 3, the sliding cam 13 is formed from a slotted-guide section 15 which is positioned in the center and two outer cam sections 14. Each outer cam section 14 comprises three cam tracks 17, by way of each of which a different valve stroke is set. As an alternative, two cam tracks can be arranged instead of three on each outer cam section 14.

As can be seen in FIG. 4 or 5, each sliding cam 13 is assigned an actuator 16 which has an extendable pin (not shown) which interacts with the slotted-guide section 15. As a result, an axial displacement of the sliding cam 13 takes place in a region between two camshaft bearings. As a result of the axial displacement of the sliding cam 13, the respective valve is actuated in a targeted manner by way of a defined cam track, with the result that a different valve stroke setting takes place. The function of the displaceable cam 13 can be designed, for example, as described in document DE 196 11 641 C1.

The sliding cam 13 which is shown in FIG. 3 comprises three cam tracks 17 which are axially displaceable for each valve. As an alternative, two cam tracks instead of three can be arranged for each valve. In each case one camshaft adjusting device 18 and one drive wheel 19 as shown in FIG. 4 are attached at one end of each camshaft 7, 8. The camshaft adjusting device 18 is actuated hydraulically or electrically, by way of which a camshaft angle is adjusted, in order to change the control times of the internal combustion engine. The drive wheel 19 is configured as a chain sprocket and serves to drive the respective camshaft. To this end, the drive wheel 19 is coupled via a drive chain (not shown) to a crankshaft (not shown) of the internal combustion engine 1.

In order to mount the camshafts 7 and 8, in each case three radial bearing devices 20 are provided, for example, which comprise a lower bearing-ring body 23 which is configured in one piece with the camshaft housing 6. In the case of an internal combustion engine of V design with 8 cylinders, four radial bearing devices 20 are provided, for example. Furthermore, each radial bearing device 20 comprises an individual bearing cap 22 which is fastened with the lower ring to the camshaft housing 6 with the aid of, for example, two bolts. As an alternative, the individual bearing caps as shown in FIG. 7 are configured in one piece with the camshaft housing 6. In this case, there is a tunnel-like radial bearing device 20 a. Here, the respective camshaft 7 or 8 is pushed in through a corresponding opening 28 for mounting on the camshaft housing 6. The sliding cams 13 are brought into position at the corresponding point between the respective radial bearing devices 20 a, in such a way that the respective camshaft 7 or 8 is then pushed into them.

The camshafts 7 and 8 are preassembled on the camshaft housing 6 and are connected to the respective camshaft adjuster 18 and the drive wheel 19. After this, there is a preassembled camshaft housing unit which is attached to the cylinder-head lower part 5 in a single mounting step.

The camshaft housing 6 comprises two end sections 24 and 25, between which two lateral walls or edge parts 26 and 27 extend. The camshafts 7 and 8 extend in the axial direction parallel to the lateral walls 26 and 27 and are delimited in the axial direction by the two end sections 24 and 25.

FIG. 4 shows a first exemplary embodiment of the present invention. FIG. 4 shows the preassembled camshaft housing 6 together with the camshafts 7 and 8. The parts cylinder-head cover 4, camshaft housing 6 and cylinder-head lower part 5 which are screwed together are shown in FIG. 2. In each case one individual sliding cam 13 is provided for each cylinder both on the inlet camshaft 7 and on the outlet camshaft 8, between which sliding cam 13 and the respective gas exchange valve in each case one roller drag lever 21 is arranged.

The sliding cams 13 which are connected fixedly to the respective camshaft so as to rotate with it make a valve stroke adjustment possible. The camshaft angle can be changed by the respective camshaft adjusting device. The camshaft 7 and 8 is driven by the drive wheel 19. Depending on the operating point of the internal combustion engine 1, targeted adjustment of the valve stroke and/or of the camshaft angle is performed, in order to achieve a best possible degree of efficiency of the internal combustion engine 1 at the respective operating point.

In the exemplary embodiment which is shown in FIG. 4 and FIG. 5, the actuators 16 are positioned laterally in the camshaft housing 6, preferably in the respective lateral wall 26 and 27. To this end, as shown in FIG. 5, in each case one corresponding opening 29 is provided on the lateral wall 26 and 27 of the camshaft housing 6, through which opening 29 the respective actuator 16 is pushed in. As a result of the lateral arrangement of the actuators 16, an overall height of the camshaft housing 6 is reduced to a minimum. An arrangement of this type is advantageous, in particular, in boxer engines, since they have cylinders which lie horizontally in the vehicle and require more installation space in the width direction than, for example, inline engines or V engines.

FIG. 6 shows a second exemplary embodiment of the present invention, in which the actuators 16 are positioned in the camshaft housing 6 above the camshafts 7 and 8. An arrangement of this type is suitable, in particular, for internal combustion engines of V design or inline design.

The alternative which is shown in FIG. 7 is suitable for both exemplary embodiments of the invention. Here, the individual bearing caps as shown in FIG. 7 are configured in one piece with the camshaft housing 6, with the result that the respective radial bearing device is of tunnel-like configuration.

A three-stage sliding-cam system for an internal combustion engine 1 with simplified assembly is provided by way of the present invention, in which sliding-cam system a sufficient bearing width of the radial bearings 20 can be provided for the camshafts 7 and 8 in the case of low or small valve and cylinder spacings. As a result of the accommodation of the actuators 16 in the camshaft housing 6, the tolerances for the function of the sliding cams 13 can be kept low, since the machining of the camshaft bearings 20 and the machining operations for receiving the actuator system and the camshaft adjusting device 18 can be carried out in one component. Moreover, the camshaft housing 6 can be delivered with the preassembled camshafts 7, 8 and actuators 16 as one unit during the production of the internal combustion engine 1. 

1.-9. (canceled)
 10. An internal combustion engine comprising: a plurality of cylinders, a crankcase, a cylinder head and a cylinder-head cover, the cylinder head being formed from a cylinder-head lower part and a camshaft housing which is positioned between the cylinder-head cover and the cylinder-head lower part, and at least one camshaft; at least one sliding cam which is configured to be displaced axially on the at least one camshaft and has a slotted-guide section for actuating gas exchange valves of the internal combustion engine; and at least one actuator with an actuable pin for bringing about an axial displacement of the at least one sliding cam; wherein the camshaft and the sliding cam are positioned in the camshaft housing, wherein the camshaft, which is mounted rotatably for valve actuation, is configured to be assembled with the axially displaceable sliding cam in the camshaft housing in such a way that the camshaft, the sliding cam and the camshaft housing form one preassembled unit which is configured to be attached to the cylinder-head lower part.
 11. The internal combustion engine as claimed in claim 10, wherein the actuator which is provided for bringing about the axial displacement of the sliding cam is arranged in a lateral region of the camshaft housing.
 12. The internal combustion engine as claimed in claim 10, wherein the camshaft housing includes a plurality of laterally positioned openings for receiving the actuator.
 13. The internal combustion engine as claimed in claim 10, wherein each sliding cam is assigned an individual actuator per cylinder for the actuation of inlet-side gas exchange valves or outlet-side gas exchange valves, the sliding cam and the actuator being positioned in the camshaft housing spatially between two bearing points of the camshaft.
 14. The internal combustion engine as claimed in claim 10, wherein at least two gas exchange valves are configured to be actuated by way of one sliding cam, wherein the slotted-guide section that is arranged on the sliding cam is positioned between two cam sections which, in each case, serve for actuating the gas exchange valves and, in each case, have a plurality of cam tracks.
 15. The internal combustion engine as claimed in claim 10, wherein a camshaft adjusting device and/or at least one drive wheel are/is attached at one end of the camshaft.
 16. The internal combustion engine as claimed in claim 15, wherein the camshaft adjusting device and the drive wheel are connected to the camshaft and are arranged in the camshaft housing in order to form a part of the preassembled unit.
 17. The internal combustion engine as claimed in claim 15, wherein the camshaft adjusting device is driven electrically.
 18. The internal combustion engine as claimed in claim 10, wherein the camshaft housing has a plurality of bearing devices for mounting a plurality of camshafts, which bearing devices are configured in one piece with the camshaft housing. 